Web dryer of the high velocity multiple nozzle, slotted orifice type



Dec. 24, 1968 D. R. HARDT 3,417,489

WEB DRYER OF THE HIGH VELOCITY MULTIPLE NOZZLE, SLOTTED ORIFICE TYPE Filed Oct. 19, 1966 III/III N INUENTOK ATTO EN EY 3,417,489 WEB DRYER OF THE HIGH VELOCITY MULTIPLE NOZZLE, SLOTTED ORKFHIE TYPE David R. Hardt, Wauwatosa, Wis., assignor to Zerand Corporation, Menomonee Falls, Wis, a corporation of Wisconsin Filed Oct. 19, 1966, Ser. No. 587,750 1 Claim. (Cl. 34160) This invention relates generally to air dryers of the type using a group of nozzles from which high velocity air jets are forced under pressure through a slotted orifice in the nozzle to impinge against the moving web or other product to be treated.

The web to be dried may be of various materials and the invention finds particular utility in drying the ink and coatings which have been applied to a paper or board web.

Because air is a relatively poor conductor of heat, the boundary layer next to the web resists the transfer of heat to the printed web, and it also resists the movement of molecules of solvent away from the evaporating surface. A high-velocity dryer disrupts the boundary layer of air, permitting rapid escape of solvent molecules and the result is greatly increased rates of heat and mass transfer, or, in other words, faster evaporation and drying.

The advantages of simple, high-velocity drying have been known and used to some extent for many years and the slotted-orifice type of air dryer was perhaps the first of the high-velocity dryers as they are known at the presout time.

This invention is in the nature of an improvement over the structure shown in the US. Patent 3,176,412 which issued to Gardner on Apr. 6, 1965, and is entitled, Multiple Nozzle Air Blast Web Drying. That patent advocates the use of a nozzle of tapered design resulting in laminar, non-turbulent flow of air.

The invention is also an improvement over that shown in Dunglers Patent Re. 24,144 of Apr. 24, 1956, entitled, Group of Nozzles for Treating Material. As taught in that patent, it was desired to avoid the formation of eddy currents, and to avoid disturbances between the zones of fiuid supply and exhaust.

The present invention relates to an improved nozzle construction which acts to amplify the turbulence of the jet and thereby considerably increase the drying efficiency of the air jet.

The construction of the nozzle is such the air under pressure is made to become turbulent prior to its issuance through the slotted, supply orifice turbulent, the air that moves towards the web in a turbulent flow, then impinges on the web; it then diffuses in a turbulent manner and in opposite directions along the web.

Another aspect of the invention relates to an improved suction outlet for the air after it has effected a drying action on the web, which suction passage acts to balance the various forces acting on the web, such as the impingement of the air jet initially, the suction effect of the exhaust passage, the web speed which creates a lifting tendency, and other factors. The results are considerably more efiiciency of the air in drying the web and prevention of web flutter.

The invention provides a dryer having an improved air supply nozzle and an improved exhaust passage, both of which cooperatively act together in efliciently causing the air to dry the solvent or other matter on the web.

These and other objects and advantages of the present invention will appear hereinafter as this disclosure progresses reference being had to the accompanying drawings in which:

FIGURE 1 is a longitudinal view of a dryer made in accordance with the present invention, certain parts being 3,4l7,489 Patented Dec. 24, 1968 shown in section for the sake of clarity in the drawings, and showing the web moving past the dryer;

FIGURE 2 is a transverse view of the dryer shown in FIGURE 1, taken generally along line 2--2 in FIGURE 1, certain parts being shown as broken away or in section for the sake of clarity in the drawings:

FIGURE 3 is a detailed, enlarged view of some of the nozzles as shown in FIGURE 1; and,

FIGURE 4 is a detailed and further enlarged view of portions of the nozzles.

Referring in greater detail to the drawings, the drying hood H includes an inner plenum IP and an outer plenum OP. The inner plenum is the supply plenum and air under pressure is supplied from conduit 1 and then enters the inner plenum. A suitable and adjustable baffle 2 is provided in conduit 1 which can be manually adjusted by the handle 3 through rod 4. The outer plenum OP is for exhausting air through the conduit 5 which also has an adjustable baffie 6 therein which can be manually adjusted by the knob 7 through the control rod 8.

Within the inner plenum is located a series of transversely extending and generally inverted U-shaped channels 10. It will be noted that these channels have substantially straight, parallel sides 10a and 10b which extend normally to the web.

The areas between the channels in the inner plenum and designated generally by the numerals 11 are the supply nozzles, and air is supplied from conduit 1 to inner plenum IP and between the channels 10 and into the nozzles 11. Reference has been made for the substantially parallel sides 10a and 10b which form the sides of the nozzle.

The channels extend across the width of the inner plenum and their open ends are in communication with the outer plenum OP. A suction or exhaust passage 12 extends transversely across the dryer at the bottom of each of the channels 10. This passage 12 is defined by two angle iron members 13 and 14 which are spaced a distance apart to form the suction passage. Thus, exhaust air from adjacent the web W enters the channels 10 through passage 12 and is then sucked to the ends of the channels 10, out chamber OP and conduit 5.

The drying gas, for convenience referred to in this disclosure as air, is supplied into the supply plenum at a pressure in the range from 3 inches to 15 inches of water, and it should further be mentioned that the dryers of the type to which the present invention relates are those which are of a minimum-maximum capacity of from generally 8,000 to 20,000 feet per minute of air at the nozzle. Thus, the present invention is concerned with problems which are found in high velocity dryers and in which the web speed may be up to 1500 feet per minute. Generally speaking, the movement of the web is about of the velocity of the air jet to be described.

Since the volume delivered from the very narrow nozzles is small, the power requirement is not excessive and the kinetic energy expended on the surface of the web is not destructive. The small volume flow from an individual nozzle has little energy in spite of the high velocity of the jet.

A supply, slotted orifice 20 is provided at the end of each nozzle 11 and is defined by the spacing between the angle irons 21 and 22 which are rigidly secured across the inner plenum. Preferably, the width of the slotted orifice, is in the neighborhood of .040 to .050 inch and I have found this distance to be particularly efficient in the drying function to be described, particularly when the nozzles are located slightly over 2 inches apart and up to two and one-half inches apart. The nozzles are preferably spaced about of an inch from the web.

The web W is preferably located a distance of about /8 to /s of an inch from the discharge nozzle.

Referring again to the discharge nozzle 11 and its slotted orifice 20, it will be noted that the nozzle 11 does not converge smoothly to its opening, but instead the angle irons provide flat obstructing surfaces 23 and 24 which terminate adjacent one another and form the elongated and narrow air supply to orifice 20. As a result, the air does not rush smoothly out of the orifice, but instead is caused to be very turbulent, as indicated at either side of the discharge opening. At lower end of the nozzle, the upper edge of the orifice 20- is formed as a radius at R, and this is important in insuring proper discharge of the air from the nozzle with the desired turbulence. The air is forced out the elongated nozzle Where it impinges directly against the moving web and then is diverted in the opposite directions along the web, as indicated by the arrows.

Because of the nozzle shape provided by the present invention and the turbulence therein, the turbulent air flows toward the web and then impinges and turns along the web. This turbulence is shown in FIGURE 4 and is in contrast to the teachings of the prior art where laminar flow is advocated along the Web. As shown in FIGURE 4, as the turbulent flow of air from the nozzle impinges on the web at point 25, referred to as a stagnation point, the air molecules become disassociated, which results in heat absorption. As the flow then diverges along the web in opposite directions, it forms a turbulent layer TL just above the boundary layer BL. The layer TL is highly turbulent due to the initial turbulence created in the air just prior to discharge from the nozzle. As this air moves along the web from its impingement point, the air molecules become reassociated which results in release of the heat previously absorbed, and this released heat is then transferred to the web through the insulating boundary layer BL, the transfer taking place due to radiation and conduction as well as by mass flow.

The more turbulent the layer TL is made, the thinner will be the boundary layer BL, and it is maintained thin and therefore less effective as an insulator, due to this high turbulence and velocity of the mass air layer TL. The pressure gradient that exists between the layer TL and layer BC, due to the turbulence of layer TL, tends to make layer BL itself turbulent.

A zero stress layer exists between the surface of the web and the boundary layer BL.

After moving along the web, the turbulent air from adjacent orifices then meets midway between the orifices, namely at the general location of the exhaust passage 12, and the air is then sucked upwardly through the passage 12 and out of the outer plenum chamber. It will be noted that the flanges 26 and 27, respectively, of angle irons 13 and 14 restrict the exhaust passage of the channel members 10, thus retarding or holding the air, and creating a balanced eifect between the supply air from the nozzle orifices 11 and the air being drawn off through exhaust passage 12. This considerably enhances the web drying action and retards the breaking up of the turbulence. The air then eventually is diffused upwardly through passage 12.

The turbulence along the web is not only enhanced but is maintained as long as possible by the particularly shaped inlet nozzle and exhaust passages and this nicety of car balance between the inlet nozzle and the exhaust passage has resulted in a marked increase in drying effectiveness. Furthermore, it has resulted in the elimination of flutter from the web and the balancing of the lifting suction effeet on the web. Stated otherwise, the area indicated generally by numeral 28 does not become a highly negative pressure area due to the shielding by flanges 26 and 27.

With the above described structure, I have found certain dimensions to be particularly desirable, for maximum drying efficiency. For example, with a spacing between the nozzle transverse center lines of from slightly Over two inches and up to two and one-half inches, a nozzle orifice width of between approximately .04 and .05 inch, and the nozzles located about of an inch from the web, the exhaust passage width is preferably in the neighborhood of %of an inch.

Various modes of carrying out the invention are contemplated as being within the scope of the following claim particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. In a web dryer of the type in which the work to be dried is advanced along a predetermined path and exposed to jets of drying gas issuing from a plurality of nozzles extending toward the work, said nozzles extending substantially the full width of the work and transversely of such path and from A; to A1 of an inch from said path, said nozzle having an open upper end and straight opposed sides arranged in parallelism and normal to said path, said nozzles also have a lower air discharge end adjacent the work and defined by generally flat, opposed obstructing surfaces which terminate adjacent one another in rounded corners to form a single, elongated and narrow air supply orifice; a supply plenum in direct air delivering communication with said open ends of said nozzles; an air exhaust suction passage between adjacent nozzles for withdrawal of gases from the surface of the work against which drying gas is directed through said nozzles, said passage being of a width of about /3 of an inch and formed as a restricted slot extending substantially the full width of the work whereby the withdrawal suction pressure along the work and between nozzles is minimized to promote turbulence of said gas, said nozzles being spaced slightly over two inches apart, and the width of the nozzle orifice is from .04 to .05 inch.

References Cited UNITED STATES PATENTS Re. 24,144 4/1956 Dungler 34-160 2,731,732 1/1956 Harris et al 34160 3,036,385 5/1962 Russell 34-460 3,041,739 7/1962 Meier-Windhorst 34160 XR 3,176,412 4/1965 Gardner 34-160 XR 3,281,957 11/1966 Ranney et a1. 34-l56 FREDERICK L. MATTESON, JR., Primary Examiner.

H. B. RAMEY, Assistant Examiner.

US. Cl. X.R. 239-568, 597 

1. IN A WEB DRYER OF THE TYPE IN WHICH THE WORK TO BE DRIED IS ADVANCED ALONG A PREDETERMINED PATH AND EXPOSED TO JETS OF DRYING GAS ISSUING FROM A PLURALITY OF NOZZLES EXTENDING TOWARD THE WORK, SAID NOZZLES EXTENDING SUBSTANTIALLY THE FULL WIDTH OF THE WORK AND TRANSVERSELY OF SUCH PATH AND FROM 3/8 TO 5/8 OF AN INCH FROM SAID PATH, SAID NOZZLE HAVING AN OPEN UPPER END AND STRAIGHT OPPOSED SIDES ARRANGED IN PARALLELISM AND NORMAL TO SAID PATH, SAID NOZZLES ALSO HAVE A LOWER AIR DISCHARGE END ADJACENT THE WORK AND DEFINED BY GENERALLY FLAT, OPPOSED OBSTRUCTING SURFACES WHICH TERMINATE ADJACENT ONE ANOTHER IN ROUNDED CORNERS TO FORM A SINGLE, ELONGATED AND NARROW AIR SUPPLY ORIFICE; A SUPPLY PLENUM IS DIRECT AIR DELIVERING COMMUNICATION WITH SAID OPEN ENDS OF SAID NOZZLES; AN AIR EXHAUST SUCTION PASSAGE BETWEEN ADJACENT NOZZLES FOR WITHDRAWAL OF GASES FROM THE SURFACE OF THE WORK AGAINST WHICH DRYING GAS IS DIRECTED THROUGH SAID NOZZLES, SAID PASSAGE BEING OF A WIDTH OF ABOUT 3/8 OF AN INCH AND FORMED AS A RESTRICTED SLOT EXTENDING SUBSTANTIALLY THE FULL WIDTH OF THE WORK WHEREBY THE WITHDRAWAL SUCTION PRESSURE ALONG THE WORK AND BETWEEN NOZZLES IS MINIMIZED TO PROMOTE TURBULENCE OF SAID GAS, SAID NOZZLES BEING SPACED SLIGHTLY OVER TWO INCHES APART, AND THE WIDTH OF THE NOZZLE ORIFICE IS FROM .04 TO .05 INCH. 